Polycarbonates derived from reactions involving organic dihydroxy compounds and carbonic acid derivatives have found extensive commercial application because of their excellent mechanical and physical properties. These thermoplastic polymers are particularly suited for the manufacture of molded products where impact strength, rigidity, toughness, thermal and dimensional stability as well as excellent electrical properties are required.
However, these polymers exhibit a brief though definite burning time when contacted with an open flame and do not meet a specified requirement for flammability resistance in applications where high temperatures and/or exposure to fire may be encountered. In addition, stabilizers or other functional additives which are normally used in polycarbonates will further modify the burning characteristics of the plastic to make them unacceptable where a certain flame retardance requirement is specified.
Also stabilizers and functional additives such as monomeric phosphates, phosphoric acid esters and thiophosphoric acid esters containing halogenated alkyl radicals have been incorporated into polymers to increase their flame resistant properties. Metal salts have also been utilized to provide flame retardance characteristics to polycarbonates. Further, in aromatic polycarbonate resins some of the phenolic diols used in the production thereof have chlorine or bromine atoms substituted on the aromatic ring to provide flame resistant characteristics to the final polycarbonate.
However, in order to obtain the flame resistant characteristics these stabilizers and halogenated phenolic diols have to be employed in such large quantities that they may reduce the desirable physical properties of the polymers such as impact strength and may even cause considerable deterioration in other physical properties such as resistance to hydrolysis. A particular disadvantage in using the halogenated diols in the synthesis of the polycarbonate is the increased cost of the final resin to an economically undesirable extent.
Illustrative of the techniques utilized to provide flame retardant characteristics to polycarbonates is U.S. Pat. No. 3,475,372.
It is thus an object of the present invention to provide an alternative by way of a copolycarbonate wherein molecular chains are incorporated units comprising sulfonylamide groups which impart an enhanced level of flame retardance to the polycarbonate.
It is a further object of the invention to provide a process by which sulfonyl amide groups are to be incorporated in the molecular structure of polycarbonates.
A plasticized polycarbonate composition comprising an aromatic polycarbonate into which admixed is an organic sulfonamide plasticizer was disclosed in British Pat. No. 2,000,515.